Modern computer systems attempt to represent human knowledge by using structured information in the form of semantic networks, terminologies, and ontologies. The human knowledge is represented using a structure that represents the “concepts” of the human knowledge and the connections between those concepts. This kind of knowledge can be conceptually structured as a mathematical graph. The “backbone” of this graph is hierarchically structured using a Directed Acyclic Graph (DAG) of concepts and “IS-A” links. An IS-A link may demonstrate that concept “B” is a kind of a (parent) concept “A.” The DAG can be augmented by lateral relationships between concepts and by local information about the concepts.